Volatile sulphur compounds (VSCs) produced by anaerobic microorganisms on the tongue are major contributors to oral malodour. Antimicrobial agents such as zinc salts may therefore indirectly reduce the production of VSCs. The aim of this study was to evaluate the effect of four zinc-containing sorbitol lozenge formulations (0.1-0.5% zinc gluconate) on oral malodour (‘morning breath’) by breath and tongue flora analysis on 24 healthy volunteers. Chlorhexidine (0.2% chlorhexidine gluconate) mouthwash was used as positive control and sorbitol lozenges as negative control. Breath odour was evaluated by a Halimeter† and organoleptic readings, and tongue flora by culture of oral microorganisms before, and at intervals over a 60 min period after, treatment. All treatments were effective in reducing sulphides in breath odour but chlorhexidine and 0.5% zinc lozenges produced the greatest reduction. All treatments produced a significant decrease (p<0.001) in bacterial counts 15 min post treatment, with chlorhexidine being most effective (p<0.05). Counts on fastidious anaerobic agar containing vancomycin correlated positively with Halimeter† readings. The combination of methods used provided a broader approach to the assessment of breath odour.Key words: oral malodour, volatile sulphur compounds, zinc, chlorhexidine, oral bacteria

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